1. Field of the Invention
The present invention relates to a radio frequency identification (RFID) tag which exchanges information with an external device in a noncontact manner and a method of manufacturing the same. In some cases, among those skilled in the technical field corresponding to the present invention, the “RFID tag” referred to in this specification is called “RFID tag inlay” as an internal constituent member (inlay) for an “RFID tag”. In some other cases, this “RFID tag” is called “wireless IC tag”. Also, this “RFID” tag comprises a noncontact-type ID card.
2. Description of the Related Art
In recent years, various types of RFID tags capable of noncontact information exchange by means of radio waves with external devices typified by reader/writers have been proposed. One of the various types of RFID tags proposed has an antenna pattern for radio wave communication and an IC chip mounted on a base sheet made of a plastic or paper. One of possible applications of such type of RFID tag is that the RFID tag is attached to an article and information about the article is exchanged with an external device for identification or the like of the article.
FIGS. 1 (A) and (B) are a front view and a sectional side view, respectively, of an example of an RFID tag.
The RFID tag 1 shown in FIG. 1 is constituted by an antenna 12 provided on a base 13 formed of a material in the form of a sheet such as a polyethylene telephthalate (PET) film, an IC chip 11 connected to the antenna 12 through bumps 16, and a cover sheet 14 bonded to the base 13 by an adhesive 15 so as to cover the antenna 12 and the IC chip 11.
The IC chip 11 constituting the RFID tag 1 is capable of exchanging information with an external device by performing wireless communication through the antenna 12.
Various applications including the above-mentioned one have been presented with respect to this type of RFID tag, which however has been hampered by high manufacturing cost. Therefore various attempts have been made to reduce the manufacturing cost of the RFID tag.
As one of the attempts to reduce the manufacturing cost, there has been pursued the idea of forming an antenna by using a paste material which is made conductive by blending a metallic filler (Ag in ordinary cases) with a resin material such as an epoxy resin (Japanese Patent Laid-Open No. 2000-311226 (paragraph [0066])). If such a paste material can be used to replace a thin sheet of a metallic material such as Cu, Al or Au, it can largely contribute to a reduction in the manufacturing cost of the RFID tag.
In manufacture of the RFID tag shown in FIG. 1, the IC chip 11 is connected to the antenna 12 formed on the surface of the base 13 formed of a PET member in the form of a sheet or the like, through the bumps (metal protrusions) 16 formed on electrodes of the IC chip 11. However, in a case where the antenna 12 is formed by printing a case material, a problem described below may arise with the connection between the IC chip 11 and the antenna 12.
FIG. 2 (A) shows a case where a metal is used as an antenna material and FIG. 2 (B) shows a case where a paste is used as an antenna material to be compared with each other.
An antenna 121 (in FIG. 2 (A)) formed of a thin sheet of a metal or an antenna 122 formed of a paste material (in FIG. 2 (B)) is formed on the base 13 formed of a PET member. The bumps 16 are formed on electrodes 111 on the IC chip 11 in each of the cases shown in FIGS. 2(A) and (B).
FIGS. 2 (A) and (B) show a state in which the IC chip 11 with bumps 16 is placed on the base 13 on which the antenna 121 or 122 is formed, the bumps 16 facing the base 13, and in which the IC chip 11 is connected to the antenna 121 or 122 through the bumps 16.
In FIG. 2, illustration of the adhesive 15 and the cover sheet 14 shown in FIG. 1 (B) is omitted. At the time of connection, the IC chip 11 is pressed from above as viewed in the figure with a jig (not shown). A pressing force is thereby applied from the bumps 16 to the antenna 121 or 122. In the case of the antenna 121 made of a metallic material as shown in FIG. 2(A), there is no problem with this pressing, since the hardness of the antenna 121 is high. In the case of the antenna 122 made of a paste material as shown in FIG. 2 (B), there is a problem described below. A swelling 122a of paste material forming the antenna 122 around the bump 16 is produced. In this case, the necessary insulation distance cannot be maintained between the IC chip 11 and the antenna 122. If this distance is changed, characteristics of the RFID tag including a wireless communication characteristic (hereinafter referred to as “tag characteristics”) are changed. This causes variations in tag characteristics when the RFID tags are mass-manufactured.
The method of mounting various types of IC chips on a circuit board apart from the RFID tag is being widely practiced. In ordinary cases, a multiplicity of bumps are formed on an IC chip and the pressing force per bump is small even when a paste material is used as a wiring material on a circuit board and, therefore, there is no serious problem due to protrusion of the paste material.
In contrast, in the case of the RFID tag, the number of bumps provided in one IC chip for connection to the antenna is about two or four, the pressing force per bump is extremely large presenting the above-mentioned problem of a swelling in paste material. In order to reduce the pressing force, it is necessary to reduce the pressing force applied when the IC chip is placed, by an apparatus for placing the IC chip on the base, to an extremely small value in comparison with the case of placing an ordinary IC chip on which a multiplicity of bumps are formed. However, considering the presence of an adhesive between the base and the IC chip, it is extremely difficult to reduce the pressing force to an extremely small value while enabling a reliable connection to be made in a short time.